This application claims priority to Italian Patent Application Serial No. RM2002A000500, filed Oct. 4, 2002, entitled xe2x80x9cUltra-Low Current Band-Gap Reference,xe2x80x9d which is commonly assigned.
The present invention is related in general to a voltage reference generator for an integrated circuit (IC), and, in particular, to a voltage reference generator for a flash memory for a portable device such as a cellular telephone.
In many integrated circuits and particularly in flash memories such as for use in cellular telephones and the like, a voltage reference generator circuit is used. The output of the voltage reference is needed in many blocks of the IC for a variety of functions. Some important requirements for a voltage reference generator for flash memories for use in portable instruments such as cellular phones include:
1. Stability over the extended temperature range from xe2x88x9240 to +85 degrees C.;
2. Stability over process parameter ranges;
3. Low voltage operation to reduce power consumption;
4. Low current drawn from the power supply in active and standby modes of operation to extend the battery life (the voltage reference circuit is generally also left on in the flash standby mode to allow fast recovery from standby); and
5. Low cost deriving from both small silicon real estate and by avoiding extra process steps needed to build non-standard devices to implement the voltage reference circuit.
One example of a design for a voltage reference circuit is the band gap voltage reference (BGVR) circuit. While this circuit has been successfully used in a number of applications, unfortunately it is not well suited for flash memory circuits in portable battery operated devices such as cellular telephones and the like, where low current consumption and low operating voltages are required for at least the following reasons:
The minimum operating Vcc power supply for a cellular telephone is increasingly very low, for example, present devices have a nominal Vcc as low as 1.42 V, ruling out many of the available variations of the BGVR;
Stability over a wide temperature range and process variations is necessary for flash memories used in portable battery operated devices. BGVRs are typically not sufficiently stable for practical needs of other parts of the memory served by the BGCR output;
The current drawn by state-of-art BGVRs is typically not less than 10 xcexcA, which is too much for a cellular telephone or similar battery operated flash memory application; and
Bipolar transistors, key components in the BGVR, such as those that are available in standard flash memory manufacturing processes, do not have adequate performances for a quality BGVR circuit.
Accordingly, what is needed is a simple band-gap voltage reference circuit for a portable flash memory device such as a cellular telephone that will work at acceptable voltages and currents over an extended temperature range and have adequate process stability, using a standard flash technology.
The above-mentioned problems with band-gap voltage reference circuits, as well as other problems, are addressed by the present invention and will be understood by reading and studying the following specification.